The present invention relates to a photo sensing device and the manufacturing method thereof, especially to a photo sensing device using surface-emitting LED as light source to increase responsive of photo receiver and prevent the short circuit of connection wires, and the manufacturing method thereof.
The photo sensing devices such as photo couplers, photo sensors are extensively used in optical-based signal transmission system such as fiber communication, mouse or computer control systems. For examples, the related technologies are disclosed in Taiwan Pat. No. 254484 with title xe2x80x9cPhoto coupler devicexe2x80x9d and 289804 with title xe2x80x9cPhoto coupler apparatusxe2x80x9d
FIG. 1A shows a top view of prior art photo sensing device and FIG. 1B shows a sectional view along line Axe2x80x94A in FIG. 1A. The photo sensing device, such as a photo coupler, comprises at least a light emitter 13 (for example, a light emitting diode, LED) and a light receiver 15 (for example, a photo diode, PD). The light emitter 13 and the light receiver 15 are fixed to two separate inner lead 139 (fourth inner lead) and inner lead 159 (first inner lead) of a leadframe. The LED 13 is connected to a sixth inner lead 137 through a connection wire 135. The anode and cathode of the PD 15 are connected to second inner lead 151 and third inner lead 157 through connection wires 153 and 155. Moreover, a semi-sphere encapsulating epoxy 17 and a sealing shell 11 are covered on the LED 13, the LD 15 and the connection wires 135, 153 and 155 to prevent short circuit of the connection wires. As indicated by the phantom line, the light generated by the LED 13 is received by the PD 15 to generate corresponding electric signal.
However, in above photo sensing device, the most light received by the PD 15 is reflection light of the LED 13. The response of the photo sensing device is deteriorated.
FIG. 2 shows a sectional view of another prior art photo sensing device, wherein the fourth inner lead 239 of the leadframe is modified to lift the position of the LED 23. The LED 23 is placed on the PD 25 mounted on the first inner lead 259. Therefore, the light-receiving area of the PD 25 is increased and the response of the photo sensing device is enhanced.
However, in above photo sensing device, the distance between the LED 25 and the PD 23 is critical. The voltage endurance and isolation is poor when the encapsulating epoxy is excessively thin. The photo response is not satisfactory when the encapsulating epoxy is excessively thick. Moreover, the encapsulating epoxy is formed after the PD 25 and the LED 23 are mounted, therefore, the connection wires 235 and 255 have the risk of short circuit.
It is an object of the prevent invention to provide a photo sensing device having an encapsulating epoxy with easily adjustable height. The voltage durability and photo response are enhanced
It is another object of the prevent invention to provide a photo sensing device, wherein the photo emitter can be easily mounted and the height of the photo emitter can be easily controlled.
In one aspect of the present invention, a surface-emitting LED with anode and cathode on same surface is mounted on a top front surface of an encapsulating epoxy. The light of the surface-emitting LED can be directly received by a photo receiver and the photo response is enhanced.
In another aspect of the present invention, the photo receiver and the connection wires thereof are enclosed by an encapsulating epoxy and then the photo emitter is mounted on the encapsulating epoxy, the short circuit problem is prevented.
The various objects and advantages of the present invention will be more readily understood from the following detailed description when read in conjunction with the appended drawing, in which: